For some reason on Windows you can't directly change .WEBP to PNG or JPG like you can with other formats, so instead open it in MSPaint then save as .PNG.
Well, at least in some of this kind of dresses where the 'skirt' part is big and puffy, women used to have lots of little bags under there to carry things, and you could make the apron into a big pocket with some basic sewing.
As for the bulge, I think the dress could hide it pretty well with a good underskirt or two.